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PG105 Convection Enhanced Pirani
Gauge
The SRS PG105 is a convection-enhanced Pirani gauge (CEPG) manufactured by Stanford Research
Systems. When used with an IGC100 controller the PG105 provides a convenient, reliable and low-cost
measurement of vacuum over a wide pressure range extending from atmosphere to 10-4 Torr.
This appendix provides a detailed description of the principle of operation, construction, gas dependence,
calibration and fundamental strengths and weaknesses of the PG105 gauge head. Application examples
and a few practical tips are provided along the way. Basic maintenance and troubleshooting information
are also included.
Since it is not possible to cover this complex gauge in such a short note, a comprehensive list of
references is provided at the end.
In This Application Note
Principle of Operation 3 Contamination 13
Cleaning 14
Construction 6 Materials 14
Calibration 8 Cleaning Procedure 14
Bakeout 15
Accuracy and Stability 9
-3
Application Examples and Tips 15
Operation Below 10 Torr 10
Safety Considerations 17
Mounting Orientation 10 Explosive Gases 17
Compression Mounts 17
Mounting Recommendations 11 Overpressure Risks 18
Handling 11
Grounding 18
Location 11
Temperature 12 Electrical Connection 19
Vibration 12
Grounding 12 PG105 Gauge Test Procedure 20
Compression fittings 12 References 21
1/8 NPT Fittings 12
Other Fittings 12
(408)744-9040 Stanford Research Systems
www.thinkSRS.com
2 PG105 Convection Enhanced Pirani Gauge
Stanford Research Systems (408)744-9040
www.thinkSRS.com
PG105 Convection Enhanced Pirani Gauge 3
Principle of Operation
The PG105 Convection Enhanced Pirani Gauge (CEPG) is a variation of the traditional
Pirani vacuum gauge design1. Pressure measurement is based on the transfer of heat from
a fine wire in the sensor to the surrounding gas 2.
Figure H-1. PG105 Convection-Enhanced Pirani Gauge
A schematic representation of the basic gauge design is depicted in Fig. H-2. The hot
wire sensor is located inside the vacuum and is one leg, Rsense, of a Wheatstone resistor
bridge. The entire bridge circuit is an integral part of the gauge head. An external
feedback amplifier3 is connected to this circuit, and balances the bridge, VNULL= 0, during
normal operation. If there are no changes in ambient temperature, the value of Rsense at
bridge 'null' is a constant, independent of pressure, and given by the product:
Rsense = Rcomp